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This study was conducted to monitor the susceptibility status of Aedes aegypti (Linnaeus) larvae in the Sunda Islands of Indonesia against various organophosphates and organochlorines. Larval bioassay was performed in accordance with the World Health Organization standard protocol. Field-collected and reference strains of Ae. aegypti larvae were tested against diagnostic doses of eight larvicides belonging to organophosphates and organochlorines, namely bromophos (0.050 mg/liter), chlopyrifos (0.002 mg/liter), fenitrothion (0.020 mg/liter), fenthion (0.025 mg/liter), malathion (0.125 mg/liter), temephos (0.012 mg/liter), DDT (0.012 mg/liter), and dieldrin (0.025 mg/liter). Mortality rates of larvae were recorded at 24-h posttreatment. This study showed that Ae. aegypti larvae from Padang, Samarinda, Manggarai Barat, and South Central Timor were susceptible to both fenitrothion and dieldrin (mortality rates ≥ 98%). About 6 out of 10 field strains of Ae. aegypti larvae were resistant (

The present study aims to investigate the susceptibility status of Aedes albopictus (Skuse) collected from residential areas in Sabah, Malaysia towards eight WHO-recommended dosages of larvicides representing the classes of organophosphates and organochlorines. Field and reference strains of Ae. albopictus larvae were bioassayed in accordance to WHO standard methods using diagnostic dosages of bromophos, malathion, fenthion, fenitrothion, temephos, chlorpyrifos, dichlorodiphenyltrichloroethane (DDT), and dieldrin. The results revealed that Ae. albopictus was resistant (mortality < 90%) towards malathion, temephos, and DDT. In addition, most of the Ae. albopictus strains exhibited a wide range of susceptibilities against bromophos, with mortality ranged from 49.33 to 93.33%. On the contrary, only dieldrin was able to induce 100% mortality against all strains of Ae. albopictus. Tolerance to fenitrothion, fenthion, and chlorpyrifos, with mortality ranging from 81.33 to 97.33%, was also observed in this study.

The Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), is considered one of the most economically damaging pests of citrus orchards in Spain. Insecticide treatments for the control of this pest are mainly based on aerial and ground treatments with malathion bait sprays. However, the frequency of insecticide treatments has been increased in some areas of the Comunidad Valenciana in the last years, because of problems with the control of C. capitata. We have found that field populations from citrus and other fruit crops from different geographical areas in Spain showed lower susceptibility to malathion (6- to 201-fold) compared with laboratory populations. More importantly, differences in susceptibility could be related to the frequency of the field treatments. A resistant strain (W), derived from a field population, and a susceptible laboratory strain (C) were maintained in the laboratory. The W strain showed cross-resistance to the organophosphate fenthion (10-fold) but not to spinosad. Enzymatic assays showed that acethylcholinesterase activity was less inhibited in vivo by malathion and in vitro by malaoxon (active form of malathion) in adult flies from the W-resistant strain. Experiments to evaluate the effects of synergists revealed that the esterase inhibitor S,S,S-tributyl phosphorotrithioate (DEF) partially suppressed malathion resistance. Thus, target site insensitivity and metabolic resistance mediated by esterases might be involved in the loss of susceptibility to malathion in C. capitata. Nonetheless, additional biochemical and molecular studies will be required to confirm this hypothesis.

Organophosphate/carbamate target resistance has emerged in Culex pipiens L. (Diptera: Culicidae), the vector of Wuchereria bancrofti and West Nile virus (family Flaviviridae, genus Flavivirus) in China. The insensitive acetylcholinesterase was detected in only one of 20 samples collected on a north-to-south transect. According to previous findings, a unique mutation, G119S in the ace-1 gene, explained this high insensitivity. Phylogenetic analysis indicates that the mutation G119S recently detected in China results from an independent mutation event. The G119S mutation thus occurred at least three times independently within the Cx. pipiens complex, once in the temperate (Cx. p. pipiens) and twice in the tropical form (Cx. p. quinquefasciatus). Bioassays performed with a purified G119S strain indicated that this substitution was associated with high levels of resistance to chlorpyrifos, fenitrothion, malathion, and parathion, but low levels of resistance to dichlorvos, trichlorfon, and fenthion. Hence, it is possible that in China, dichlorvos, trichlorfon, and fenthion will still achieve effective control even in the presence of the G119S mutation.

The toxicities of 44 plant essential oils against larvae of Cadra cautella (Walker) were examined using direct contact and vapor phase toxicity bioassays and compared with the lethal activity of chlorpyrifos-methyl, diazinon, dichlorvos, and fenthion, four widely used organophosphorus insecticides. Responses varied according to plant material used and exposure dose and time. In a filter paper contact toxicity bioassay, potent toxicity was produced from buchu leaf, niaouli, and rosemary oils at 2.4 mg/cm2 and armoise, cypress, galbanum, and mace oils at 4.7 mg/cm2. In vapor phase toxicity bioassays with larvae, cypress, galbanum, niaouli, and rosemary oils were much more effective in closed containers than in open containers, indicating that the lethal effects of these oils were largely because of action in the vapor phase. As judged by 24-h LC50 values, potent fumigant action was observed with niaouli oil (64.7 mg/liter air) and rosemary oil (64.6 mg liter/air). Cypress and galbanum oils exhibited weak fumigant activity. These essential oils were less active than dichlorvos (0.86 mg/liter air). Little or no fumigant action was observed with chlorpyrifos-methyl, diazinon, and fenthion. Essential oils described herein, particularly niaouli and rosemary oils, merit further study as potential larvicides for the control of C. cautella.

The rate and extent of dermal absorption are important in the analysis of risk from dermal exposure to toxic chemicals and for the development of topically applied drugs, barriers, insect repellents, and cosmetics. In vitro flow-through cells offer a convenient method for the study of dermal absorption that is relevant to the initial processes of dermal absorption. This study describes a physiologically based pharmacokinetic (PBPK) model developed to simulate the absorption of organophosphate pesticides, such as parathion, fenthion, and methyl parathion through porcine skin with flow-through cells. Parameters related to the structure of the stratum corneum and solvent evaporation rates were independently estimated. Three parameters were optimized based on experimental dermal absorption data, including solvent evaporation rate, diffusivity, and a mass transfer factor. Diffusion cell studies were conducted to validate the model under a variety of conditions, including different dose ranges (6.3-106.9 microg/cm2 for parathion; 0.8-23.6 microg/cm2 for fenthion; 1.6-39.3 microg/cm2 for methyl parathion), different solvents (ethanol, 2-propanol and acetone), different solvent volumes (5-120 microl for ethanol; 20-80 microl for 2-propanol and acetone), occlusion versus open to atmosphere dosing, and corneocyte removal by tape-stripping. The study demonstrated the utility of PBPK models for studying dermal absorption, which can be useful as explanatory and predictive tools that may be used for in silico hypotheses generation and limited hypotheses testing. The similarity between the overall shapes of the experimental and model-predicted flux/time curves and the successful simulation of altered system conditions for this series of small, lipophilic compounds indicated that the absorption processes that were described in the model successfully simulated important aspects of dermal absorption in flow-through cells. These data have direct relevance to topical organophosphate pesticide risk assessments.

The flavin-containing monooxygenase gene family (FMO1-6) in humans encodes five functional isoforms that catalyze the monooxygenation of numerous N-, P- and S-containing drugs and toxicants. A previous single nucleotide polymorphism (SNP) analysis of FMO1 in African-Americans identified seven novel SNPs. To determine the functional relevance of the coding FMO1 variants (H97Q, I303V, I303T, R502X), they were heterologously expressed using a baculovirus system. Catalytic efficiency and stereoselectivity of N- and S-oxygenation was determined in the FMO1 variants using several substrates. The I303V variant showed catalytic constants equal to wild-type FMO1 for methimazole and methyl p-tolyl sulfide. Catalytic efficiency (V(max)/K(m)) of methyl p-tolyl sulfide oxidation by R502X was unaltered. In contrast, methimazole oxidation by R502X was not detected. Both H97Q and I303T had elevated catalytic efficiency with regards to methyl p-tolyl sulfide (162% and 212%, respectively), but slightly reduced efficiency with regards to methimazole (81% and 78%). All the variants demonstrated the same stereoselectivity for methyl p-tolyl sulfide oxidation as wild-type FMO1. FMO1 also metabolized the commonly used insecticide fenthion to its (+)-sulfoxide, with relatively high catalytic efficiency. FMO3 metabolized fenthion to its sulfoxide at a lower catalytic efficiency than FMO1 (27%) and with less stereoselectivity (74% (+)-sulfoxide). Racemic fenthion sulfoxide was a weaker inhibitor of acetylcholinesterase than its parent compound (IC(50) 0.26 and 0.015 mM, respectively). The (+)- and (-)-sulfoxides were equally potent inhibitors of acetylcholinesterase. These data indicate that all the currently known FMO1 variants are catalytically active, but alterations in kinetic parameters were observed.

A gas chromatographic (GC) method was developed and statistically validated for the simultaneous determination of residues of pyrethroid, endosulfan, and organophosphorus insecticides and some of their metabolites on olive tree leaves. Pesticide residues were extracted by static extraction with acetone–dichloromethane. After evaporation of the extract to dryness and redissolution in acetone, the organophosphorus insecticides were determined by GC with nitrogen–phosphorus detection. Another portion of the extract, after solvent change to acetonitrile, was cleaned up on an Alumina-N cartridge and analyzed for insecticides sensitive to electron-capture detection (ECD), i.e., pyrethroids and endosulfan and its metabolite. Recoveries of the organophosphorus insecticides ranged from 80.7 to 93.3% with relative standard deviations (RSDs) of ≤ 7.2%; recoveries of the ECD-sensitive insecticides ranged from 71.6 to 89.5% with RSDs of ≤ 11.6%. The method was used to analyze 26 samples of olive tree leaves from organic olive groves all over Greece, and the results confirmed the viability of the method for routine analysis. Residues of fenthion and fenthion sulfoxide were found in one and 3 samples, respectively, and their identities were confirmed by GC with mass spectrometry.

A sample of Aedes aegypti (L.) from Santiago de Cuba, Cuba, with a high level of temephos resistance (19.58x at the 50% lethal concentration [LC50]), was subjected to temephos selection to evaluate the utility of this organophosphate insecticide for mosquito control. High resistance developed after six generations of selection (200.00x). Little or no cross-resistance was observed to the organophosphates, malathion and fenitrothion, but high cross-resistance was observed for the pyrethroid deltamethrin (337.5x) and the organophosphate fenthion (12.74x). Synergism tests implicated detoxifying esterases in temephos and fenthion resistance and deltamethrin resistance was associated with a cytochrome P450 monooxygenasa. Biochemical tests, polyacrylamide gel electrophoresis (PAGE), and inhibition studies confirmed the presence of elevated esterase activity associated with temephos resistance. Pyrethroid resistance could be associated with a glutathione-S-transferase mechanism but not the esterases. The cross-resistance to deltamethrin from temephos selection could limit the use of both insecticides for Ae. aegypti control.

Four strains of Aedes aegypti (L.), one from Cuba and three from Venezuela, were bioassayed for susceptibility to eight insecticides, including the organophosphates, temephos, malathion, fenthion, pirimiphos methyl, and chlorpyrifos, and the pyrethroids, deltamethrin, lambda cyhalothrin and cypermethrin, S, S, S,-tributyl phosphorotrithioate and piperonyl butoxide were used as synergists to assess the involvement of esterases and monooxygenases in organophosphate resistance. Venezuelan strains had low levels of resistance to fenthion and malathion, and moderate to high resistance to temephos, pyrimphos methyl, and chlorpiriphos. All strains were susceptible to the pyrethroids, except the Cuban strain, which had moderate levels of resistance to cypermethrin. Organophosphate resistance in Ae. aegypti is a serious threat to control operations. Integrated strategies for Ae. aegypti control to prevent or delay pyrethroid resistance in Venezuela and Cuba are discussed.

Studies were conducted between 1993 and 1996 using 3 natural grape vine populations, 1 susceptible laboratory strain, and 1 resistant selected strain of Drosophila melanogaster L. In vitro monooxygenase activity (ethoxycoumarine-O-deethylation) (ECOD) was recorded from microsomal fractions of all strains. Results varied over a 6-fold range between susceptible laboratory Canton and resistant selected RDDT strains and over a 2-fold range between the Canton strain and natural populations of flies. Few significant variations of ECOD activity were detected among the natural populations despite many insecticide treatments, but activities were significantly correlated with toxicological tolerance to 5 of the 15 insecticides (deltamethrin, fipronil, chlorpyriphos ethyl, DDT, and diazinon). Moreover, immunoblotting responses of microsomal protein encoded by Cyp6A2 showed that the levels of expression were quantitatively correlated with toxicological tolerance to almost the same group of insecticides (deltamethrin, fipronil, chlorpyriphos ethyl, DDT, fenvalerate, and fenthion). However, the level of CYP6A2 expression in some natural strains (still weakly resistant) was almost comparable with one of the resistant strains. In vivo monooxygenase activity recorded in individual abdomens of flies showed that frequency distributions of ECOD activity in natural populations overlapped those of the resistant and laboratory strains, which were much narrower. Substantial and fast frequency changes (of the narrowness) that obtained in laboratory were related to either the time of rearing of 1 of the natural populations or selecting this population with an insecticide that has a toxicology correlated with both of the monooxygenase signs measured. Perspectives on using the CYP6A2 expression and ECOD activity for detecting a resistance mechanism by cytochrome P450 in field populations are discussed.

The Pto gene was derived originally from the wild tomato species Lycopersicon pimpinellifolium and confers resistance to Pseudomonas syringae pv tomato strains expressing the avirulence gene avrPto. The Fen gene is also derived from L. pimpinellifolium and confers sensitivity to the insecticide fenthion. We have now isolated and characterized the alleles of Pto and Fen from cultivated tomato, L. esculentum, and designated them pto and fen. High conservation of genome organization between the two tomato species allowed us to identify the pto and fen alleles from among the cluster of closely related Pto gene family members. The pto and fen alleles are transcribed and have uninterrupted open reading frames that code for predicted proteins that are 87 and 98% identical to the Pto and Fen protein kinases, respectively. In vitro autophosphorylation assays revealed that both the pto and fen alleles encode active kinases. In addition, the pto kinase phosphorylates a previously characterized substrate of Pto, the Pto-interacting Pti1 serine/threonine kinase. However, the pto kinase shows impaired interaction with Pti1 and with several previously isolated Pto-interacting proteins in the yeast two-hybrid system. The observation that pto and fen are active kinases and yet do not confer bacterial speck resistance or fenthion sensitivity suggests that the amino acid substitutions distinguishing them from Pto and Fen may interfere with recognition of the corresponding signal molecule or with protein-protein interactions involved in the Pto- and Fen-mediated signal transduction pathways.

The catalytic activity and amino acid specificity of the tomato Pto and Fen kinases were investigated. The Pto and Fen genes were fused to the carboxyl terminus of the maltose-binding protein and expressed in Escherichia coli. Incubation of the purified fusion proteins with [gamma-32P]ATP in an in vitro assay showed that both proteins were capable of autophosphorylation. Mutant fusion proteins in which the conserved lysine residue of subdomain II was changed to a glutamine were unable to autophosphorylate. Phosphoamino analysis of the active fusion proteins indicated that both kinases phosphorylate serine and threonine residues but not tyrosine.

A novel transient gene expression system was used to study both the tomato disease resistance gene Pto and a Pto homolog designated Fen. The gene expression system was based on potato virus X (PVX). Tomato plants that were both susceptible to strains of Pseudomonas syringae pv tomato carrying the corresponding avirulence gene avrPto and insensitive to the insecticide fenthion were infected with in vitro-generated transcripts of PVX derivatives containing either Pto or Fen. Expression of the Pto gene from the virus genome failed to elicit P.s. tomato resistance, indicating that the PVX system is not suitable for the study of Pto. However, expression of the Fen gene resulted in sensitivity to fenthion. The utility of the PVX gene expression system was further demonstrated through structure/function studies of the Fen gene. A correlation was shown between Fen protein kinase activity and the ability of this protein to confer fenthion sensitivity to tomato. Furthermore, it was demonstrated that mutation of a putative N-terminal myristoylation site, proposed to be involved in membrane targeting, rendered the Fen protein inactive. Analysis of a Pto-Fen chimeric gene allowed the fenthion sensitivity domain to be localized to the C-terminal part of the Fen protein. Interestingly, expression of the Fen kinase from the PVX genome in Nicotiana spp resulted in a fenthion-independent necrotic response. Our results support the involvement of the Fen gene in a signal transduction pathway(s).

We have employed a genetic approach to study the resistance of tomato to the phytopathogenic bacterium Pseudomonas syringae pv tomato. Resistance to P. s. tomato depends upon expression of the Pto locus in tomato, which encodes a protein with similarity to serine/threonine protein kinases and recognizes pathogen strains expressing the avirulence gene avrPto. Eleven tomato mutants were isolated with altered resistance to P. s. tomato strains expressing avrPto. We identified mutations both in the Pto resistance locus and in a new locus designated Prf (for Pseudomonas resistance and fenthion sensitivity). The genetic approach allowed us to dissect the roles of these loci in signal transduction in response to pathogen attack. Lines carrying mutations in the Pto locus vary 200-fold in the degree to which they are susceptible to P. s. tomato strains expressing avrPto. The pto mutants retain sensitivity to the organophosphate insecticide fenthion; this trait segregates with Pto in genetic crosses. This result suggested that contrary to previous hypotheses, the Pto locus controls pathogen recognition but not fenthion sensitivity. Interestingly, mutations in the prf locus result in both complete susceptibility to P. s. tomato and insensitivity to fenthion, suggesting that Prf plays a role in tomato signaling in response to both pathogen elicitors and fenthion. Because pto and prf mutations do not alter recognition of Xanthomonas campestris strains expressing avrBsP, an avirulence gene recognized by all tested tomato cultivars, Prf does not play a general role in disease resistance but possibly functions specifically in resistance against P. s. tomato. Genetic analysis of F2 populations from crosses of pto and prf homozygotes indicated that the Pto and Prf loci are tightly linked.

Drift residues of naled and fenthion, which were applied for mosquito control, were sampled with α-cellulose pads in pineland and hammock ecosystems of the Florida Keys in 1989. These included habitats of state and federally protected insect and cactus species on wildlife refuges with no-spray zones. Naled residues were detected up to 750 m downwind in a no-spray zone in pinelands 6 h after application to adjacent target areas. Fenthion residues were detected up to 50 m downwind in hammock 15 min after application to adjacent target areas. In controlled residue degradation experiments, technical naled did not disappear significantly from pads suspended vertically from wires or laid flat on the substrate over a 240-min period. Fenthion did not disappear significantly from pads laid on the substrate but did disappear partly from pads suspended from wires. Estimated environmental concentrations of naled and fenthion in these habitats may be used to calculate ecological risk indexes for protected species.

Ear tag eflBcacy studies were conducted on 4 pastured herds (18-37 head/herd) of dairy heifers and dry dairy cows at the Beltsville Agricultural Research Center. The herd of dry cows served as a control and received no fly control treatment. Each of the three herds of dairy heifers were tagged (2 tags/head) with either Cutter Gold, Cutter Blue, or an experimental tag containing 10% cyfluthrin during the 2nd wk of Jun. Fly density was determined by making weekly counts on 15 head of face flies/face, horn flies/side, and stable flies on front legs. Three or 4 pretreatment and 15 or 16 posttreatment counts were made.

The Toyama strain of Culex tritaeniorhynchus Giles collected and colonized in Japan was highly resistant to organophosphorus insecticides. Resistance ratios were more than 125,000 for temephos, 6,000 for malathion, 26,500 for fenitrothion, and 22,929 for fenthion. Resistance was incompletely dominant over susceptibility. Insensitivity of acetylcholinesterase to the compounds was the major factor of resistance. The insensitivity index for paraoxon was 734 in comparison with a standard susceptible (Taiwan) strain. There was also evidence for detoxification by carboxylesterase. Two carboxylesterase genes and one gene coding a major molecular species of acetylcholinesterase were all located on chromosome II. These multiple enzymatic factors acted together, indicating a single gene for resistance on chromosome II, when the Toyama strain was crossed with susceptible marker mutants without recombination of the chromosome.

Sixteen samples of Culex tritaeniorhynchus Giles collected in 14 prefectures in Japan in 1984 were assessed for resistance to insecticides. All of the samples were highly resistant to organophosphorus (OP) and carbamate insecticides, but none was resistant to a pyrethroid (permethrin). Resistance levels for each of the OP's and carbamates were similar among samples except for diazinon and temephos. Considerable variation in LC50's of temephos may have resulted from exposure to other OP's used for crop protection because temephos has not been used in ricefields in Japan. A uniform susceptibility to permethrin accorded with lack of a history of pyrethroids as agrochemicals. Insensitivity of acetylcholinesterases (AChE's) was the principal factor regulating resistance to OP's. Mosquitoes with such insensitive AChE's began to appear in ca. 1978 and rapidly replaced most of the susceptible mosquitoes within 2 or 3 yr. Since 1980 C. tritaeniorhynchus has become more abundant, and some resurgence in human cases of Japanese encephalitis has occurred at the same time. However, a recurrence of an epidemic of the magnitude of those experienced in the 1960s is implausible because of changes in agriculture and demography.

Against chironomids, 6 applications of 1% G chlorpyrifos at 0.11–0.28 kg AI/ha during May–Sept. 1977, and one of 10% CR pellets at 1.12 kg AI/ha in Sept. 1977 were made to partial or entire areas of 2 man-made lakes. The effectiveness of chlorpyrifos against Chironomus utahensis (Malloch), C. decorus Johannsen, Procladius freemani Sublette, and P. sublettei Roback, gradually declined; a rate of 0.11 kg Al/ha was highly effective in May, but in Sept., the granules even at 0.28 kg Al/ha as well as the CR pellets did not give an effective midge control. Pre-, and posttreatment laboratory bioassays conducted on field-collected larvae revealed a shift in susceptibility of midge larvae to chlorpyrifos, temephos, malathion, and fenthion. In Sept.–Oct. 1977, C. utahensis showed 4½-fold resistance to chlorpyrifos and 3-fold to temephos, while C. decorus developed 10-fold resistance to chlorpyrifos and >2- to 4-fold to the other 3 OPs. Resistance in Procladius spp. ranged from 7-fold to malathion to several hundred fold to temephos. Two of the 4 new synthetic pyrethroids tested in the laboratory were highly active against these midges.

Studies in 3 successive years with Procambarus clarki (Girard) in rice fields showed significant reductions in rice seedling establishment when the associations were both as natural and confined populations. The natural infestations resulted in seedling reductions of 70 to 100%, whereas confined crayfish caused losses in seedlings ranging from 9% at 0.34 crayfish per m2 to 94% at 2.4/m2. Methyl parathion at 566.5 g/ha was highly effective in controlling P. clarki and Orconectes virilis (Hagen). Fenthion at 112.1 g/ha resulted in high mortality of the former species but not the latter.

Macrocyclops albidus were exposed for 24 hours to ABATE®, fenthion, malathion, methyl parathion, and chlorpyrifos at concentrations of 1, 5, 10, 25, and 50 parts per billion (ppb). Exposure to chlorpyrifos resulted in the greatest mortality to M. albidus; concentrations of 25 and 50 ppb caused 100% mortality. The thermal tolerance was lowered significantly by all chemicals at concentrations from 1 to 50 ppb.

Several gas chromatographic (GC) methods for analyzing fenthion were studied, and flame ionization detection, a glass column packed with SE-52 on Chromosorb GHP, and on-column injection were selected as parameters. No suitable internal standard was found because of coeluting, bias-producing impurities in fenthion. Several liquid chromatographic (LC) methods were also studied, and UV detection, a Zorbax ODS column, and a methanol-water-H3P04 mobile phase were finally selected as parameters. Dipentyl phthalate was selected as internal standard. After testing, this LC method was submitted for collaborative study. During the collaborative study, the manufacturer found an impurity, 3-methyl-4-(methylthio)anisole, co-eluting with fenthion in the collaborative method. The manufacturer's method was then evaluated as an alternative for collaborative study, but a significant unidentified impurity from the formulation blank, used for formulating emulsifiable concentrates, was also found co-eluting with fenthion. The anisole impurity was verified by LC, and the presence of the S-isomer and bis-methylthio-fenthion impurities was found by gas chromatographic- mass spectrometric (GC-MS) analyses. An anisole material obtained from Mobay was also verified by GC-MS analysis. Several other impurities were identified from literature references and from private communication with the manufacturer.

A broad spectrum of resistance to organophosphorus insecticides has evolved in Bemisia tabaci (Gennadius) in southern California. High resistance to sulprofos and methyl parathion, ranging from 20- to 54-fold, was detected in three field populations. The resistance is related to exposure to chemicals used for control of cotton pests. Moderate levels of resistance (3- to 7-fold) were observed to fenthion, malathion, and parathion in the strain from Imperial Valley, California. In addition, two strains showed relatively high levels of resistance to permethrin (12- to 29-fold). Resistance to DDT (6.5- to 9.7-fold) was present in all three strains.

A mixed population of Culex tarsalis Coquillett, Culex quinquefasciatus Say, Culex peus Speiser, and Culex erythrothorax Dyer breeding in a sewage-treatment lagoon was subjected with increasing frequency to treatments with organophosphate larvicides during 1981–84. C. tarsalis , rare in 1981 (9% of total), had become the most abundant species by 1984 (84% of total), displaying high levels of larval resistance to chlorpyrifos (64-fold), methyl parathion (57-fold), temephos (42-fold), fenthion (41-fold), and malathion (36-fold).

The effect of recommended dosages of trichlorfon, fenthion, famphur, and phosmet on physiological and nutritional indices of steers infested and not infested with Hypoderma spp. were evaluated under laboratory conditions. The parameters used as indicators of general stress were heart and respiration rate, rectal temperature, blood cholinesterase, blood urea nitrogen, serum glutamic oxalacetic transaminase, serum creatine phosphokinase and packed cell volume. Feed utilization indices included dry matter and nitrogen digestibilities. Heart rates, respiration rates, and rectal temperatures increased rapidly after treatment of grub-free steers and returned to normal within 3 h after treatment. Treatments of grub-infested steers with trichlorfon and phosmet resulted in significantly increased respiration rates, and rectal temperatures were significantly increased after exposure to trichlorfon, phosmet, and fenthion. Treatment with phosmet significantly reduced heart rates through 1 week after treatment. Blood cholinesterase levels were decreased after all treatments and blood urea nitrogen was significantly lowered after treatments with trichlorfon, famphur, and phosmet.

Gambusia affinis were exposed to the insecticides ABATE®, fenthion, chlorpyrifos, methyl parathion, and malathion for 24 h at concentrations of 1, 5, and 10 ppb and for 48 h at 5 ppb. The thermal tolerance was lowered significantly for male and female G. affinis by the toxicants methyl parathion and chlorpyrifos at 5 and 10 ppb with 24 h exposure. Activity was restricted with fish exposed to methyl parathion and chlorpyrifos at concentrations of 10 ppb for 24 h and at 5 ppb for 48 h.

Populations of Aedes aegypti (L.) from 28 sites in Caribbean islands and neighboring countries were tested during 1983–85 for larval resistance to temephos, malathion, fenthion, and propoxur. Nearly all populations displayed somewhat elevated LC95 values toward temephos. In two cases, Tortola and Antigua, susceptibility to this widely used larvicide was 47.4- and 46.8-fold lower than normal, indicating presence of significant resistance; operational importance of this resistance requires investigation. Fenthion resistance was recorded in most collections but at lower levels than for temephos. Malathion resistance was likewise low and present in only 10 of the sites sampled. Some propoxur resistance was found in nearly all samples, but maximal levels (in Granada) did not exceed 10.8-fold. Selection of a synthetic population of A. aegypti from various countries by temephos pressure in the laboratory produced 104.3-fold resistance within 19 generations, thus indicating that risk for organophosphate resistance in this important vector species requires serious consideration.

Three week old tadpoles of Hyla regilla were exposed to the insecticides temephos, fenthion, methyl parathion, chlorpyrifos, and malathion for 24 h at concentrations less than and at field applied rates as recommended for mosquito control in California. The thermal tolerance was significantly lowered by all chemicals and concentrations tested. Chlorpyrifos and methyl parathion were the most active compounds tested whereas malathion was the least toxic to H regilla tadpoles. Activity was depressed, in comparison to control tadpoles, by the chemicals methyl parathion (100 ppb) and malathion (500 ppb).

Laboratory experiments were conducted to determine the relative toxicity of certain insecticides, herbicides, and fungicides to the vegetative growth and zoospore production in North Carolina (NC) and Louisiana (LA) isolates of Lagenidium giganteum. Zoospore production in both isolates was less tolerant than mycelial growth to most of the pesticides tested and, thus, the IC50 values (inhibition concentration) for mycelial growth rate on agar underestimated toxicity. The most toxic pesticides to one or both isolates of L. giganteum were captan, gamma-BHC. DDT. toxaphene. chlorpyrifos, and fenthion. These pesticides produced at least 10% inhibition of mycelial growth rate or completely inhibited zoospore production at concentrations below 5 parts per million (ppm). The least toxic pesticides caused a 10% inhibition in mycelial growth rate and failed to inhibit zoospore production at concentrations greater that 50 ppm. These were diflubenzuron. permethrin. temephos. and propoxur (LA isolate only). Pesticides of intermediate toxicity were: malathion, carbaryl, methoprene, alachlor, and atrazine. The two isolates differed substantially in their tolerance of the following pesticides: malathion, chlorpyrifos, toxaphene, carbaryl. propoxur. permethrin. and methoprene. At their recommended rates of application for control of mosquito larvae, methoprene, fenthion, malathion, and temephos would probably be compatible with both isolates of L. giganteum.

Experimental selection of insect cultures with insecticides to develop resistance in the laboratory is reviewed. Aedes, Culex, Musca , and Heliothis are considered because they are the insect genera most commonly used in experimental selection. When the rates at which resistance developed are compared, resistance to the axonic poisons DDT and permethrin is found to have developed more rapidly than resistance to malathion, parathion, and other acetylcholinesterase inhibitors. The degree to which resistance developed in the laboratory was usually equaled or exceeded in field collections within one decade of the laboratory experiments. Procedures are suggested for laboratory selection for resistance as a component of a resistance risk assessment system. The relevance of the experimental results to actual development of resistance in the field must be assessed by determining whether common genetic mechanisms are involved. This information is available in the literature but will require the tedious tracking of genetic strains used in experimental selection and subsequently used in studies of genetic and biochemical mechanisms. Such an undertaking was beyond the scope of the present review.

Fenthion ( O,O -dimethyl O -[4-(methylthio)- m -tolyl] phosphorothioate) applied by airplane at a rate of 56.0 g/ha (20.8 ml mixed in one liter fuel oil) to control mosquito larvae on 14,164 ha of mountain meadow ranchland in the Little Laramie Valley, Wyoming, had relatively little adverse effect on honey bees, Apis mellifera L. Although the material is highly toxic to the bees, exposed colonies had only partial, nonincapacitating loss of the field force that lasted only one day. Brood production, number of frames of adult bees, and pollen collection were not affected. Therefore, in a similar situation, it would not be necessary or practical for a commercial beekeeper to move his colonies during application of this insecticide.

A strain of Amblyseius fallacis (Garman) from Belding, MI, with a 75-fold resistance to azinphosmethyl and a 120-fold resistance to diazinon was strongly cross-resistant to parathion and dimethoate, moderately cross-resistant to azinphosethyl, malathion, phosmet, methyl parathion, fenitrothion, fenthion, demeton, and phosphamidon, and slightly cross-tolerant to carbophenothion, phosalone, ethion, and tepp. When crossed and back-crossed with a susceptible strain, azinphosmethyl-resistance proved to be partially dominant and showed a clear segregation indicating that it was principally due to a single gene allele.

A highly active esterase associated with resistance to temephos, chlorpyrifos, parathion, methyl parathion, malathion, and fenthion in the southern house mosquito from California is coded by a single gene with 2 alleles: Est-BA , coding a strongly staining esterase; and Est-BO , coding a weakly staining esterase. Est-BA was found to be dominant over Est-BO . Est-B gene is localized on the same chromosome as the gene coding resistance and there is a strong possibility that these 2 genes are identical since no recombinants were observed.

Effects on birds of an aerial application of fenthion, a potent organophosphorus cholinesterase (ChE)-inhibiting insecticide, were assessed on four study sites 1.8 to 3.6 km2 in size. These sites were located within 121.5 km2 of wet meadows treated with 47 g of fenthion (AI) per ha in ultra-low-volume formulation. Assessment methods were searches for sick or dead birds, measurements of brain ChE activity in specimens found dead or collected alive at different time intervals, and counts of bird populations. After treatment, 99 birds and 15 mammals were found sick or dead; 106 of these were on one site. Brain ChE activity in dead birds was depressed sufficiently to indicate that death was caused by an anti-ChE substance. Brain ChE activity in three common bird species collected alive showed the greatest reduction 2 days postspray. Two of these species had ChE activity that was still significantly ( P

A method intended for regulatory purposes is described for the determination of organophosphorus insecticide residues in fruits and vegetables. Eighteen organophosphorus insecticides, azinphos-ethyl, chlorpyrifos, diazinon, dichlorvos, dimethoate, ethion, ethoate-methyl, fenitrothion, fenthion, formothion, malathion, methidathion, mevinphos, parathion, phosalone, phosphamidon, thiometon, and trichlorphon, and 7 metabolites, fenitrooxon, fenthion sulfoxide, fenthion sulfone, malaoxon, desethylphosphamidon, thiometon sulfoxide, and thiometon sulfone, were extracted from different crops with acetone and partitioned into hexane or ethyl acetate, according to their polarities. The hexane extract was cleaned up by eluting from a Florisil column with acetone-hexane (4+96). The ethyl acetate extract needs no cleanup. The concentrated extracts were analyzed by gasliquid chromatography using thermionic detectors. Recoveries conducted at fortification levels ranging from 0.1 to 2 mg/kg were in most cases above 80%. The limit of sensitivity is less than 0.1 mg/kg.

High levels of resistance (>1000-fold) to the juvenoid methoprene have been induced in a dimethoate-resistant laboratory strain as well as in a field multiresistant strain of Musca domestica L. by exposure of mature larvae to methoprene-treated pupation medium. Resistance extended also to 3 other juvenoids tested. However, cross resistance to dimethoate, fenthion, parathion, and Isolan (1-isopropyl-3-methyl-5-pyrazolyl dimethylcarbamate), originally present in the dimethoate-R strain, has declined during the course of selection by methoprene.

A broad spectrum of resistance to organophosphorus insecticides has evolved in Culex pipiens quinquefasciatus (= fatigans) Say in California’s San Joaquin Valley. Resistance levels determined on F1 larvae following control failures by chlorpyrifos, involve Abate® ( O, O′ -(thiodi- p -phenylene) O, O, O′O′ -tetramethyl phosphorothioate) at a level of 116.7 times the normal LC50, chlorpyrifos 52.2×, fenthion 48.9×, methyl parathion 24×, malathion 16.4×, and parathion 12.9×. Such multiresistance had appeareel earlier in 2 other major species, Aedes nigromaculis (Ludlow) and Culex tarsalis Coquillett, and is related to the multitude of chemicals employed in mosquito control and agriculture. Resistance in larvae is almost entirely overcome by the synergist DEF ( S, S, S -tributyl phosphorotrithioate) but is unaffected by piperonyl butoxide. Thus, hydrolytic esterases and not mixed function oxidases are implicated as primary resistance mechanisms. Certain synthetic pyrethroids, derivatized carbamates, insect growth regulators, and a biodegradable DDT analogue have demonstrated high activity against the resistant population.

Data are presented for 14 insecticides found systemically active in screening tests with arthropods parasitizing guinea pigs. Thirty-five insecticides were administered to small groups of cattle, and the following treatments afforded forded >90%systemic control of cattle grubs, Hypoderma spp.: Bay 37342 (O,O-dimethyl O .[4-(methylthio)-3,5-xylyl) phosphorothioate) as 0.1 and 0.25% sprays (22 and 50 mg/kg); bromophos-ethyl, 15 mg per kg by capsule; fenthion as 0.05, 0.1, and 0.25% sprays (12, 20, and 50 mg/kg); Imidan® ( O,O -dimethyl S -phthalimidomethyl phosphorodithioate) in feed for 10 days at 1.5 and 2 mg per kg per day and as a 0.25% spray (50-55 mg/kg); menazon in feed for 10 days at 2.5 and 5 mg per kg per day, as 0.5 and 0.75% sprays (100 and 155 mg per kg), and as a pour-on of 15% in oil (100 mg/kg); Shell SD-8447 (2-chloro-1-(2,4,5-trichlorophenyl) vinyl dimethyl phosphate) as a pour-on of 16% in oil (100 mg/kg)-and as 3 applications of 0.5% spray (115 mg per kg; Shell SD-8448 (2-chloro-1-(2,4,5-trichlorophenyl) vinyl diethyl phosphate) as a 1% spray (145 mg/kg); and Stauffer R-3828 ( S -( P -chloro- alpha -phenylbenzyl) O,O -diethyl phosphorodithioate) in feed at 2.5 mg per kg per day for 10 days.

The effectiveness of 3 organic phosphorus compounds (coumaphos, fenthion, trichlorfon) against the common cattle grub. Hypoderma lineatum (de Villers), and the cattle grub, H. bovis (L.), was investigated. A 133-day feedlot trial consisted of 216 calves used in 6 feed-additive treatment groups, 1 pour-on treatment group, and a control group. Forty-four additional calves received 3 pour-on treatments in a separate 133-day trial. The control group (48 animals) averaged 20 grubs per head. All 6 feed additive treatments and the 4 pour-on treatments significantly (P < 0.05) reduced the number of grubs present, as compared with an average of the peak grub count of individual animals in the control group. The reductions of grub counts by the feed additive treatments were: 3 mg per kg and 4 mg per kg coumaphos daily. 6 days-56%, 90%; 1 mg per kg and 1.5 mg per kg fenthion daily, 6 days-92 %, 98%; and 2 mg per kg and 3 mg per kg fenthion daily, 3 days-86%, 90%. The pour-on treatments, applied once at a rate of Y2 fl oz per 100 lb, gave results as follows: 8% and 12% trichlorfon—96%, 95%; and 1 % and 2% fenthion—77%, 85%. When the percent control by the various treatments is considered in conjunction with the number of animals free of grubs throughout the trial and those with a peak count of fewer than 5 grubs per head, it appears that fenthion feed additives at 1.0 mg per kg and 1.5 mg per kg per day for 6 days and trichlorfon pour-ons (8%, 12%) were the most satisfactory treatments. No significant differences in total weight gain or overall feed efficiency existed among the treatment groups and the control group. The usual better performance by steers as compared with heifers was observed, but sex of animal had no effect on grub counts.

Five insecticides, some in different formulations, were tested for their effects on predator populations and plant bugs in cotton fields. The materials fell into 4 groups according to toxicity to predators: (1) high toxicity: fenthion emulsifiable concentrate (EC) and trichlorfon EC; (2) moderate toxicity: trichlorfon ultra low volume (ULV); (3) low toxicity: dimethoate, disulfoton, fenthion ULV, and propoxur; and (4) limited toxicity: trichlorfon 50% SP. The sensitivity of the predators to the insecticidal applications were in the following order: (1) high sensitivity: Orius insidiosus (Say) and Hippodamia convergens Guerin Meneville; (2) high 10 moderate sensitivity: Coleomegilla maculala (Dc Geer): (3) moderate sensitivity: Nabis roseipennis Reuter, N. alternatus Parsley, N. americoferus Carayon, Geocoris punctipes (Say), and Chrysopa spp.; (4) low sensitivity: Scymnus spp. and the spider complex. The spider complex was much less sensitive to insecticidal applications than were the other predators. The best plant bug control was obtained with dimethoate and fenthion EC. Dimethoate appeared to be much less toxic to the predator populations than fenthion EC.

Twenty-seven insecticides applied to artificially infested cattle as sprays and 3 applied as sprays and dips were evaluated for control of the cattle tick, Boophilus annulatus (Say), and the southern cattle tick, B. microplus (Canestrini). Effectiveness was determined by inhibition of production of viable eggs by female ticks that were adults or nymphs at the time of treatment. A 0.06% coumaphos suspension was used as a standard of comparison for the sprays; the following materials were equal to or more effective than the standard: 0.25% Bay 37341 ( O, O -diethyl O -[4-(methylthio)-3,5-xylyl] phosphorothioate), 0.25% Bay 39007 ( O -isopropoxyphenyl methylcarbamate), 0.25% bromophos-ethyl, 0.3% Ciodrin® ( alpha methylbenzyl 3-hydroxycrotonate dimethyl phosphate), 0.15% dioxathion, 0.1% Dowco® 175 (2,4-dichlorophenyl propyl methylphosphoramidate), 0.1% Dursban® ( O, O -diethyl O -3,5,6-trichloro-2-pyridyl phosphorothioate), 0.1% fenthion, 0.125% Imidan® ( O, O -dimethyl S -phthalimidomethyl phosphorodithioate), 0.45% Shell SD-8447 (2-chloro-1-(2,4,5-trichlorophenyl) vinyl dimethyl phosphate), and 0.1% Shell SD-8448 (2-chloro-1-(2,4,5-trichlorophenyl)-vinyl diethyl phosphate). Freshly charged vats containing 0.25% carbaryl or Shell SD-8447 controlled ticks satisfactorily; the same insecticides were less satisfactory after 6 weeks of aging and moderate use. Outstanding control was obtained throughout 42 weeks with Dursban in a vat which contained 0.11% active ingredient initially and 0.03% finally.

All Anastrepha suspense (Loew) exposed for 1 hour in tractor-trailers and aircraft to 5- to 6-hour-old residues of micronized dusts (1 or 2 g/1000 ft2) containing resmethrin, bromophos, chlorpyrifos, fenitrothion, fenthion, or Mobam® (benzo[b]thien-4-yl methylcarbamate), or to combinations, some of which contained d-trans allethrin, were dead within 24 hours. These dust also produced 100% mortality within 24 hours when the insects were exposed for ½ hour at the time of application. Other dusts produced 90% or higher knockdown in both types of exposure and were more effective than the standard, DDT + carbaryl. Aerosol formulations of d- trans allethrin (11% at rates of 30 and 10 g/1000 ft3) and of resmethrin (7.5% at a rate of 30 g) caused better than 80% knockdown in ½ hour and 99% mortality in 24 hours; however, residues of resmethrin aerosol delivered at a rate of 10 g/1000 ft3, though it produced 99–100% mortality in 24 hours in both the tractor trailers and the aircraft, had a knockdown at ½ hour of only 63–69%.

Small groups of cattle in Texas were treated dermally with systemic insecticides in the summer and checked in the fall to determine whether larvae of Hypoderma lineattun (de Villers) had been controlled. Cattle treated with trichlorfon (½ oz/cwt of an 8 or 16% pour-on or 1 gal/animal of 1% whole-body spray) had 95-100% fewer grubs than untreated cattle. Cattle treated with fenthion (½ oz/cwt of a 2% pour-on or 1 gal/animal of a 0.05 or 0.1% spray) had only 74-79% fewer grubs than the controls. Imidan® ( O,O -dimethyl S-phthalimidomethyl phosphorodithioate) as a pour-on gave better than 90% control at dosages of 13 mg/kg or more and less than 90% control at dosages of 7-13 mg/kg; generally, control was related to the amount of active ingredient per animal. Famphur administered as a pour-on (½ oz/cwt of 12.5%) gave 93% control; ½ that dosage gave 72% control. Coumaphos administered in May, June, July, or August gave 90-99% control as a 0.375% spray (1 gal/animal) and 80-95% control as a 4% pour-on (½ oz/cwt). Crufomate administered in the same months gave 90-99% control as an 8% pour-on (1 oz/cwt); a 0.5% spray (1 gal/animal) gave 50% control when administered in July but 81-89% control when applied in May, June, or August. Trichlorfon, also adminstered in the same months, gave 86-99% control as a 1% spray (1 gal/animal); an 8% pour-on (1 oz/cwt) gave 92-93% control after treatment in May, June, or July but only 68% control after administration in August. In general, lower control figures are the result of finding large numbers of grubs in 1 or 2 of the 4-5 cattle treated each month.

Insecticides were fed to dairy cattle to face-fly-larvicide subsequent manure. Effectiveness was tested by introducing first-instar larvae. Effective were zinc oxide (40 mg/kg body weight); fenthion, barthrin, dimethrin, and 3-4 dimethyl benzyl ester of chrysanthemumic acid (10 mg/kg); coumaphos (0.25 to 10 mg/kg); ronnel (1 mg/kg); and Bayer 22408 (naphthaloximido-O,O-diethyl phosphorothioate) (0.25 and 1 mg/kg). Bacillus thuriugiensis, ground Ryania speciosa stem (wood (alkaloid ry anodine) C25H35O9N or C20H37O9N), carbaryl, methoxychlor, malathion, diazinon, and sodium zirconium lactate were ineffective at dosages tested.

Polyvinyl chloride (PVC) pellets containing diazinon, dichlorvos, dimethoate, and dimetilan, and acetone solutions of these insecticides were added directly to cattle manure and fed to cattle to determine effectiveness against larvae of Musca autumnalis De Geer in manure. All insecticides in PVC or in acetone solution were very effective when added directly to manure, producing 100% mortality at 0.0003% in manure. Dimetilan in acetone solution produced 95% mortality at 0.000003%, and diazinon and dichlorvos produced 92 and 100% mortality, respectively, at 0.00003%. Insecticides in acetone solution, fed at 5 mg/kg per day, were not effective larvicides in manure. However, at the same dosage in PVC pellets, these insecticides except dimethoate + fenthion and trichlorfon produced 100% mortality through 4 days after termination of treatment. Diazinon and dichlorvos in PVC, the most promising materials, were effective through the last feeding day at 0.5 mg/kg per day. In further feeding trials with PVC-diazinon and PVC-dimetilan, reduction of pellet size, simultaneous with increasing the number of pellets fed, improved the larvicidal effectiveness of diazinon, but not of dimetilan. Increasing the number of pellets fed, by decreasing the concentration of insecticide in PVC, increased the effectiveness of dimetilan but did not alter the effectiveness of diazinon. Rate of passage of PVC-insecticide pellets through the bovine digestive tract increased with decreasing specific gravity. One-eighth-inch cubes and 1/16-inch cubes, which had almost identical passage rates, were found to pass through more rapidly than 1/32-inchcubes. Time of maximum excretion of PVC-insecticide pellets in manure was not necessarily the time of greatest mortality because of loss of insectide from the PVC pellets and subsequent degradation while in the digestive tract. Shell Chemical Company Animal Health Product V-13 dichlorvos-PVC, fed to a dairy herd for an entire summer at ¼ mg/kg per day, did not control face fly larval development in manure. There was no detectable toxicity to the catlle or residues of dichlorvos in milk.

Ronnel, butonate, Ruelene® ( O -4- tert -butyl-2-chlorophenyl O -methyl methylphosphoramidate), Bayer 29493 ( O, O -dimethyl O -[4-(methylthio)-, m -tolyl] phosphorothioate), Bayer 22408 (naphthalimido- O, O -diethyl phosphorothionte), Bayer 34098 ( O ,(4-methylthio- m -tolyl) dimethyl phosphinothioate) and Bayer 37342 ( O, O -dimethyl O -(3,5-dimethyl-4-methylthiophenyl) phosphorothioate) were mixed in poultry-growing mash at 50, 100, 200, 400, and 800 p.p.m. and fed to 5- to 7-week-old broilers for 7 days. Bayer 22408, Bayer 29493, Bayer 34098, and Bayer 37342 at all concentration levels in the feed resulted in 100% control of house fly ( Musca domestica L.) in the feces. Ronnel was effective at the 200, 400, and 800 p.p.m. levels, but was ineffective at the lower concentrations against house fly larvae; butonate and Ruelene were ineffective. Polymer and nonpolymer formulations of Bayer 22408 in the feed were equally effective against 1- and 3-day-old house fly larvae in poultry droppings. Negative gains in weight were observed of birds receiving Bayer 29493 and Bayer 37342 at 200 p.p.m. or higher in the feed. Fifty per cent of the broilers died that were on feed containing 400 or 800 p.p.m. Bayer 37342.

The organophosphorus compounds cythioate ( O,O -di-methyl O-p -sulfamoylphenyl phosphorothioate), famphur, and fenthion were administered intravenously, subcutaneously, and orally at varying concentrations to 101 female rabbits. Cholinesterase (ChE) activity levels of both plasma and red blood cells were tested, as was tick and mosquito ChE, at various times before and after dosage. These determinations measured the inhibition of ChE activity caused by pesticidal action. Correlations between fluctuations in blood ChE activity of the host and ChE activity of the ectoparasites were observed. Mortality of ectoparasites commenced at 32% ChE activity depression, and there was 100% mortality at 68% ChE activity depression. No mortality of ectoparasites occurred between the 24- and 96-hour postdosage period. Mated female ticks exposed to sublethal doses of pesticide did not lay eggs. Reduction in temperature was fatal to mosquitoes that had received sublethal doses of pesticide in their blood meal. Reproductive capabilities of rabbits were not impaired by therapeutic dosages of the pesticides.

The following 16 insecticides were found to be active in screening tests for animal systemic insecticides: Bayer 54203 (O, O -dimethyl phosphorothioate O -ester with 5-chlo-rosalicylonitrile), Bayer 62863 (2,3-dihydro-2-methyl-7-ben-zofuranyl methylcarbamate), Bayer 64995 (O, O -dimethyl phosphorothioate O, O -diester with 4,4′-dithiodiphenol), Bayer 65258 (O -ethyl S -methyl phosphoramidothioate), Chipman RP-13072 (O, O -dimethyl phosphorodithioate S -ester with 2-[(2-mercaptoethyl) thio[- N ,2-dimethylpropionamide), Dowco® 182 (2,4-dichlorophenyl dimethyl phosphate), Dowco® 183 (2-chloro-4- tert -pentylphenyl methyl methylphosphoramidate), Monsanto CP-40507 (O -phenyl methylphosphonothioate O-ester with p-hydroxybenzonitrile), Schering 34615 (m -cym-5-yl methylcarbamate), Stauffer B-9625 (O, O -dimethyl S -[ (2-methyl-1,3-oxathiolan-2-yl) methyl] phosphorodithioate), Stauffer B-10094 (O -ethyl phenylphosphonothioate O -ester wtih p-hydroxyben-zonitrile), Stauffer B-11163 (O, O -dimethyl phosphorothioate, O -ester with 4-hydroxy- m -anisonitrile) Stauffer N-4328 (O -methyl S-p -tolyl ethylphosphonodithioate), Stauffer N-4548 (S .[[ (p-chlorophenyl) thio]methyl] O -methyl methylphosphonodithioate), Union Carbide UC-8454 (5,6,7,8-tetrahydro-1-naphthyl methylcarbamate), and Velsicol FCS-303 (O -(4-bromo-2,5-dichlorophenyl) O -ethyl phenylphos-phonothioate). Of 28 systemic insecticides administered to cattle to controll larvae of cattle grubs, Hypoderma spp., the following treatments gave better than 90% control: Bay 64995 by capsule (10 mg per kg); famphur in feed for 10 days at 5 mg per kg per day; fenthion as a 0.05% spray (12 mg per kg); Imidan® (O, O -dimethyl S -phthalimidomethyl phos-phorodithioate) as 1 or 2 sprayings of 0.25% (60 mg per kg); menazon in feed for 10 days at 1 mg per kg per day and as 0.5% (120 mg per kg) and 0.25% (60 mg per kg) sprays; Stauffer B-9627 (O, O -dimethyl phosphorodithioate S -ester with mercapto-2-propanone diethyl mercaptole), by capsule (10 mg per kg); and Stauffer B-10094 as a 0.5% spray (60 mg per kg).